The present invention relates to control systems for appliances having a time controlled program cycle and in particular relates to domestic washing appliances such as dishwashers and clothes washers.
In providing cycle control systems for such appliances, it is known practice to employ electro-mechanical programmers employing a synchronous timing motor to drive an electrical programmer comprising series of ratchets or cam actuated devices for opening and closing sets of suitable electrical contacts for controlling the various functions of the machine in accordance with a predetermined program cycle. In the presently commercially available versions of such appliances, the cam or ratchet mechanism may be selectively advanced manually by the machine operator to a desired point in the cycle program prior to energizing the program timing motor.
Such cycle programming control mechanisms have found widespread use by virtue of their low initial cost, and ability to reliably switch relatively heavy currents such as the starting current associated with the appliance drum drive or pump motor. Thus, the electro-mechanical appliance programmer has maintained its popularity due to its low cost with respect to its ability to switch relatively high electrical currents.
Efforts to provide all-electronic timing control and switching functions for such appliance programmer have met with the difficulties in providing solid state switching devices capable of handling the necessary motor starting currents, yet operate from the low voltage direct current signals available from solid state logic circuits. Thus, although the electro-mechanical programmer timer is somewhat bulky and requires several moving parts, it has maintained its popularity as a low cost timing device capable of switching motor starting currents.
However, in appliances having electro-mechanical programmers it has been desired to find a way or means for the machine operator to selectively vary the time schedule of the program.
If an alternate or varied program schedule for the appliance is desired with an electro-mechanical timer, it is necessary to have an additional timing ratchet wheel and cams which may be engaged and prepositioned by the machine operator to provide the alternate program schedule. In order to provide such an alternate program schedule, the additional cost and complexity of the electro-mechanical timer has rendered such additional programming prohibitive in cost with respect to the design and manufacture of the programmer timer. Thus, it has been long desired to provide a simple yet low cost way of varying the program schedule of an electro-mechanical programmer timer without requiring additional cams or ratchets for each alternative schedule.